U.S. Published Application 2005/0020926A1, incorporated by reference herein, discloses a scanning beam imager which is reproduced in FIG. 1 herein. The imager may be used in applications in which cameras have been used in the past. In particular it may be used in medical devices such as video endoscopes, laparoscopes, etc.
FIG. 1 shows a block diagram of one example of a scanned beam imager 102′. An illuminator 104′ creates a first beam of light 106′. A scanner 108′ deflects the first beam of light across a field-of-view (FOV) 111′ to produce a second scanned beam of light 110′, shown in two positions 110′a and 110′b. The illuminator 104′, first beam of light 106′ and scanner 108′ assembly may be generally designated 109′. The scanned beam of light 110′ sequentially illuminates spots 112′ in the FOV 111′, shown as positions 112′a and 112′b, corresponding to beam positions 110′a and 110′b, respectively. While the beam 110′ illuminates the spots 112′, the illuminating light beam 110′ is reflected, absorbed, scattered, refracted, or otherwise affected by the object or material in the FOV 111′ to produce scattered light energy. A portion of the scattered light energy 114′, shown scattered from spot positions 112′a and 112′b as scattered energy rays 114′a and 114′b, respectively, travels to one or more detectors 116′ that receive the light and produce electrical signals corresponding to the amount of light energy received. Image information is provided as a serial data stream, where locations in the data stream correspond to positions in the scan pattern. The electrical signals may be transmitted to an image processor 118′ that assembles the values in the data stream into a digital image. The image processor 118′ may transmit the digital image for further processing, decoding, archiving, printing, display, or other treatment or use via interface 120′.
Illuminator 104′ may include multiple emitters such as, for instance, light emitting diodes (LEDs), lasers, thermal sources, arc sources, fluorescent sources, gas discharge sources, or other types of illuminators. Illuminator 104′ may include, in the case of multiple emitters, beam combining optics to combine some or all of the emitters into a single beam. Illuminators 104′ may also include beam-shaping optics such as one or more collimating lenses and/or apertures. Light beam 106′, while illustrated as a single beam, may comprise a plurality of beams converging on a single scanner 108′ or onto separate scanners 108′.
In a scanned beam imager (SBI), a beam director may be formed as a scanning reflector or reflectors operable to oscillate in periodic motion to reflect a beam of light in a periodic pattern. According to an embodiment, a beam director may be formed as a resonant device. According to an embodiment, a beam director may be driven to oscillate such that its velocity varies approximately sinusoidally in time and across a corresponding periodic scan pattern. One example of a beam director comprises a MEMS scanner capable of periodic deflection at a frequency near a mechanical resonant frequency. The resonant frequency may be determined by the torsional or bending stiffness of a torsion arm or cantilever arm, the moment of inertia of the oscillating body incorporating the reflector, and/or other factors such as material stiffness, processing parameters, device temperature, ambient pressure, etc.
In one example, a MEMS scanner oscillates about two scan axes that may be orthogonal. In an example, one axis is operated near resonance while the other is operated substantially off resonance. Such a case may include, for example, the nonresonant axis being driven to achieve a triangular or a sawtooth velocity profile. In another example, both axes may be operated near different resonant frequencies to produce, for example, a Lissajous scan pattern.
As illustrated in FIG. 2, a scanned beam source 201′ may comprise a meniscus objective lens or dome 212′ having a reflective surface 212′. The reflective surface 214′ may be integral to the dome 212′, such as located on the lens surface as shown in FIG. 2, or it may be suspended from or mounted on the incident side of the dome. The dome 212′ optionally has optical power and shapes and/or refracts the scanned beam 110′ as it passes through the dome. The beam 208′ emitted from the optical fiber 204′ is directed to the reflector 214′ via a shaping optic 210′. As shown in FIG. 1, a portion of the radiation reflected/scattered from the FOV 111′, travels to one or more detectors that receive the light and transmit it to a detector element 116′ that produces electrical signals corresponding to the amount of light energy received. The receiving fiber array 115′ may comprise an annular bundle of fine optical fibers generally oriented parallel to the central axis of the SBI.
It has been observed that the corners and edges of the FOV 111′ in exemplary devices may be relatively dark, even in systems where the illuminating beam 110′ dwells in these regions for a longer time as a result of the sinusoidal angular deflecting movement of a resonant mirror 108′. This darkening may be associated both with lack of detection sensitivity at wide angles and/or the cosn falloff of illumination in an optical system.